a Noise-level contours are graphical representations of noise levels on a map, similar to elevation contours on a topographic map. Noise-level contours are lines that join points of equal sound levels. Areas between given noise-level contour lines would have a noise level between the two contour values. The U.S. Department of Transportation, Federal Aviation Administration (FAA) has identified DNL 65 dB as the highest threshold of airport noise Exposure that is normally compatible with indoor and outdoor activity associated with a variety of land uses, including residential, recreational, schools, and hospitals.

b Estimates are for areas surrounding airport property of 250 of the largest civil airports with jet operations in the United States. They exclude Exposure to aircraft noise within an airport boundary.

c 1975 Exposure estimates were made by the U.S. Environmental Protection Agency. 1980–2011 estimates were made by Federal Aviation Administration.

NOTES

Noise Exposure people data for 2000 and forward was re-estimated using an enhanced version of U.S. MAGENTA (Model for Assessing the Global Exposure of Noise because of Transport Airplanes). The enhanced version of the model uses radar-based traffic data to account for unscheduled operations including freight, General Aviation and military operations. The enhanced U.S. MAGENTA also includes improvements to the acoustical model to account for differences in the sound attenuation characteristics between wing-mounted and tail-mounted aircraft engines. These enhancements result in computed population noise Exposure estimates that are more accurate and larger than previous versions of the model. Therefore, it is important to note that the "growth" in the number of people exposed from 1999 to 2000 resulted from improvements in measurement, not deterioration in aviation noise trends. In 2013, Federal Aviation Administration has revised the reporting of noise exposure from calendar year to fiscal year going back to 2000 to align with other agency performance metrics.